I asked my cat, and she said "No." Actually, I pointed my TV remote control at her. Didn't bat an eyelash. What gives cats their superior night vision is a higher density of light-sensitive rod cells as suggested by Cal, and a special reflective layer in the retina called the tapetum. This layer reflects light back the way it came, like a bicycle reflector, giving the sensitive rods cells another shot at detecting it.

On a related note, I recall watching a show on TLC or Discovery that stated that, while cats have superior low-light vision, their vision isn't as "sharp" as a human's. How one tests this sort of thing, I have no idea. Anyone have any info on this?

So what type of vision do cats possess that allows them to stare into space and watch something that none of us humans in the room under normal light see nothing at all? Do cats possess any rods or cones sensitive to ghosts and other manifestations?

And have you seen the size of those pupils? My cat's eyes can go from a tiny slit to almost total blackness with harly an iris to be seen; it's probably, fully dilated, a bigger aperture than my own, even though my eye a fair bit larger.

Cats actually have rather poor visual acuity. Ever notice how cats key to movement? They can't resolve distant objects very well at all and it is the movement of that object that will clue them in that something is there.

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Visual acuity is the ability to see the details of an object separately and unblurred. Acuity is measured in "cycles per degree", which means how many lines you can distinguish as being separate in a degree of the visual field. Humans see 30 cycles per degree, horses 18, dogs 12 and cats 6. Acuity in dogs is 0.4 times that of people, 0.67 times that of horses, and twice that of cats. Acuity in cats is 0.2 times that of people, 0.33 times that of horses, and 0.5 times that of dogs. If normal human vision is 20/20, then that of the dog between 20/50 to 20/100, the horse 20/33, and that of the cat is 20/100. However, it is difficult to measure acuity in animals so studies have often shown wide variations in results.

It might be worth noting that some animals do "see" in the infrared spectrum. I say "see" (with the quotes) because it is not done with their eyes but specialized heat sensors. How this information is presented in their mind I have no clue. Snakes have these sensors. Their ability to "see" heat differs among different snakes with it being most highly developed in Pit Vipers. I do not know if all snakes can do this or just some nor can I think of other animals that might have this ability.

I asked my cat, and she said "No." Actually, I pointed my TV remote control at her. Didn't bat an eyelash.

In a very slightly more scientific version of this test, I've taken a picture of my cat with the night vision feature of my digital camera. It uses two bright infrared LEDs to illuminate out to a range of ten feet or so. At a distance of a couple of feet, the cat's pupils remained fully dilated in the photo, indicating that she wasn't perceiving any bright lights.

Note that this isn't a particularly conclusive test as vision in the near-infrared isn't very useful. Those cool photos of heat leakage from houses and thermal gradients in the body are taken using equipment sensitive to the "far" infrared (where "far" is shorthand for me being to lazy to look up the actual wavelength). So even if a cat were able to perceive the radiation from a remote control, that wouldn't translate into the ability to see prey in the dark.

However, we can make some guesses about the cat's ability to see into the far infrared. Equipment that does so is usually cooled to reduce noise. A cat's body temperature is normally somewhat higher than a human's. So it would probably be too warm to detect faint thermal images with any reliability.

Thing is, I don't think there is a chemical in any mammalian eye that can absorb infrared wavelenghts in a way that allows for visual stimuli. The opsins (pigment proteins in the rods and cones) are all coupled to 11-cis-retinal, (retinals are aldehyde versions of vitamin A), which is converted to all-trans retinal by visual light at wavelengths that depend on the opsin. If my memory serves me, the three types of cones have different absobtion peaks: mid-to-high 500's corresponding to red, low-to-mid 500's corresponding to green, and mid 400's corresponding to blue (all numbers in nm). The rods...err, they have rhodopsinm which is a purplish pigment easily bleached by light, and are not involved with color vision, but more with seeing in dark conditions (red light in dark rooms tends not to bleach rhodopsin easily, hence it's usefulness under those conditions). It should be noted that the peak absorbtion peaks of the opsins do not correspond to the actual emitted or reflected light of colored objects; but the rather complex interplay of nervous impulses from different cone cells absorbing light of various wavelengths gives us the sense of color.

From what I understand, genetic variation can affect the total amount and absorbtion spectrum of each opsin, meaning different people literally see different things (and we won't even try to consider what different people's brains do with that info.)

UV is largely absorbed by retinal tissue before it can trigger reactions in opsins, I think, and is more damaging than anything. IR doesn't cause the right reaction, and in excessive amounts can also be damaging, obviously.

It's hard to know how vision differs from cat-to-cat, as it's pretty tough to ask them. From what I understand, what opsins and cells they have in the retina quite resemble corresponding pigments and cells in our own repertoire, though they appear to be more perceptually sensitive to the bluer end of the spectrum than the redder end, and what colors they do see have much less saturation, for reasons I never knew or have forgotten. It's probably as much or more a neurological issue as a physiological one.